[FIX] Do not raise an error if the next todo isn't found to set the previous todo...

[FIX] Do not raise an error if the next todo isn't found to set the previous todo's status

The previous line hardly makes any sense, so clarification: finding the 'next' todo is based on todo states, so until we've set the state of the todo item we've just executed (aka the previous todo) it remains the 'next' todo as well.

So in order to set the previous todo's state, we look for the next todo (which it still is) and set its state, actually marking it as the 'previous' todo

bzr revid: xmo@openerp.com-20101108104412-bd7bf3k7c5p5jkpl